Sizes

Every Shibui download has a folder for each screen. Open the folder that matches your device and use the picture inside.

Folder Use it for
MacBook The screen of any MacBook (Air or Pro).
5K Monitor A separate monitor: 27-inch screens like Apple's Studio Display, and most regular widescreen monitors.
6K Monitor Large 32-inch 6K monitors, like Apple's Pro Display XDR.
iPhone Any iPhone. It also works on most Android phones.
iPad Any iPad. The picture is square, so it fills the screen upright and sideways.

Not sure? On a Mac, use MacBook for the built-in screen and 5K Monitor for a separate monitor. If your monitor is 6K, use 6K Monitor for the sharpest picture.

How to set it. Mac: open System Settings > Wallpaper and add the picture. iPhone and iPad: save the picture to Photos, then set it as your wallpaper.

Exact sizes, for those who want them: MacBook 2880 x 1864, 5K Monitor 5120 x 2880, 6K Monitor 6016 x 3384, iPhone 1290 x 2796, iPad 2732 x 2732 pixels.